Rolling bearing for sliding door

ABSTRACT

A rolling bearing for a sliding door includes an inner ring, an outer ring, a plurality of rolling elements arranged in a rollable manner in an annular space between the inner ring and the outer ring, and a jacket member formed of a resin composition and provided so as to cover the outer peripheral surface of the outer ring. The resin composition contains polyamide 66 and aramid fiber. The polyamide 66 has a number average molecular weight of 34000 to 60000. The number average molecular weight is measured by gel permeation chromatography using hexafluoroisopropanol (HFIP) as a solvent and poly (methyl methacrylate) (PMMA) as a reference material. The content of the aramid fiber is 5 to 25 mass %.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2017-146524 filed onJul. 28, 2017 including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a rolling bearing for a sliding door.

2. Description of the Related Art

In an automobile including a sliding door, a rolling bearing for asliding door is mounted on the sliding door in order to support a smoothopening and closing operation of the sliding door. The rolling bearingfor a sliding door is also referred to as a door roller. As the rollingbearing for a sliding door, there is proposed, for example, a rollingbearing for a sliding door in which a jacket member using a polyacetalresin or a polyamide resin is provided on an outer peripheral side of anouter ring (see, for example, Japanese Patent Application PublicationNo. 11-351249 (JP 11-351249 A) and Japanese Patent ApplicationPublication No. 2007-315483 (JP 2007-315483 A)).

The rolling bearing for a sliding door that is provided with the resinjacket member is excellent in its quietness and does not require a guiderail. Therefore, the cost can be reduced. In this respect, there is anincreasing need for the rolling bearing for a sliding door. The jacketmember is required to have high durability because the jacket member isbrought into rolling contact with a vehicle body every time the slidingdoor is opened or closed. It is desirable to reduce the cost by reducingthe number of steps for painting the sliding door. Therefore, thesliding door is required to be painted by passing through a paintingline with the rolling bearing for a sliding door mounted on the slidingdoor. Thus, the rolling bearing for a sliding door is required to passthrough a high-temperature painting furnace (for example, lower than200° C.) without problems.

The rolling bearing for a sliding door that uses the polyacetal resinfor the jacket member has durability. However, the melting point of thepolyacetal resin is as low as about 165 to 175° C. Therefore, therolling bearing for a sliding door that uses the polyacetal resin forthe jacket member is melted when passing through the painting furnace.Thus, the sliding door cannot be painted by passing through the paintingfurnace with the rolling bearing for a sliding door mounted on thesliding door.

In the rolling bearing for a sliding door that uses the polyamide resinfor the jacket member, the polyamide resin tends to excel the polyacetalresin in heat resistance. Therefore, the melting of the jacket membercan often be avoided even when the sliding door is painted with therolling bearing for a sliding door mounted on the sliding door. When thesliding door is painted by this method, however, creep of the jacketmember cannot be avoided. A load caused by the self-weight of thesliding door is applied to the jacket member under a high-temperatureatmosphere. Therefore, the occurrence of the creep of the jacket memberhinders the smooth opening and closing operation of the sliding door. Inorder to avoid the creep when the polyamide resin is used for the jacketmember, the inventors have contemplated mixing reinforcing fiber in aresin composition that forms the jacket member. However, the inventors'investigation reveals that the wear resistance of the jacket memberdeteriorates and the durability decreases when the reinforcing fiber issimply mixed.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a rolling bearingfor a sliding door that includes a jacket member in which sufficientdurability (wear resistance) can be secured while providing heatresistance and creep resistance that allow the sliding door to bepainted by passing through a painting furnace at a treatment temperaturelower than 200° C.

A rolling bearing for a sliding door according to one aspect of thepresent invention has the following features in its structure. That is,the rolling bearing for a sliding door includes an inner ring, an outerring, a plurality of rolling elements arranged in a rollable manner inan annular space between the inner ring and the outer ring, and a jacketmember formed of a resin composition and provided so as to cover anouter peripheral surface of the outer ring. The resin compositioncontains polyamide 66 and aramid fiber. The polyamide 66 has a numberaverage molecular weight of 34000 to 60000. The number average molecularweight is measured by gel permeation chromatography (GPC) usinghexafluoroisopropanol (HFIP) as a solvent and poly (methyl methacrylate)(PMMA) as a reference material. A content of the aramid fiber is 5 to 25mass %.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a sectional view illustrating a rolling bearing for a slidingdoor according to one embodiment of the present invention;

FIG. 2 is a diagram for describing an evaluation method adopted inperformance evaluation; and

FIG. 3 is a graph illustrating results of the performance evaluation.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below with referenceto the drawings. FIG. 1 is a sectional view illustrating a rollingbearing for a sliding door according to one embodiment of the presentinvention. A rolling bearing 10 for a sliding door according to thisembodiment includes an inner ring 2, an outer ring 3, rolling elements4, a cage 5, and hermetic seals 6 and 7. The rolling elements 4 arearranged in a rollable manner in an annular space between the inner ring2 and the outer ring 3. The cage 5 retains the rolling elements 4. Thehermetic seals 6 and 7 seal the annular space. The rolling bearing 10for a sliding door further includes a jacket member 8 provided so as tocover the outer peripheral surface of the outer ring 3. The outerperipheral surface of the outer ring 3 has a groove 3 a along acircumferential direction. Therefore, it is possible to reduce theoccurrence of a case where the jacket member 8 provided so as to coverthe outer peripheral surface of the outer ring 3 deviates in an axialdirection (lateral direction in FIG. 1). The rolling bearing 10 for asliding door is mounted on a sliding door such that the inner ring 2 isattached to a support shaft (not illustrated) of the sliding door. Inthe rolling bearing 10 for a sliding door in which the inner ring 2 isattached to the support shaft of the sliding door, the jacket member 8is brought into contact with a mating member. Through rotation of theouter ring 3 relative to the inner ring 2, the jacket member 8 slides ina rollable manner relative to the mating member.

In the rolling bearing 10 for a sliding door, the jacket member 8 isformed of a resin composition containing polyamide 66 and aramid fiber.The polyamide 66 is a polymer having an amide bond (—NHCO—) in itsbackbone chain and consisting of a hexamethylene unit and an adipic acidunit. Examples of the polymer include a polymer obtained bypolycondensation of hexamethylenediamine and adipic acid. In theembodiment of the present invention, the polyamide 66 only needs to be aresin containing polyamide 66 at a ratio of 95 mol % or more withrespect to 100 mol % of the entire unit. The polyamide 66 may be notonly a homopolymer of polyamide 66 but also a copolymer of polyamide 66and a copolymerizable monomer or a macromolecular compound obtained bylinking polyamides 66 via a condensation agent.

In the rolling bearing 10 for a sliding door according to thisembodiment, the polyamide 66 contained in the resin composition thatforms the jacket member 8 is polyamide 66 having a large molecularweight. The polyamide 66 has a number average molecular weight of 34000to 60000. This number average molecular weight is measured by gelpermeation chromatography (GPC) using hexafluoroisopropanol (HFIP) as asolvent and poly (methyl methacrylate) (PMMA) as a reference material(the number average molecular weight measured by this method ishereinafter referred to also as a number average molecular weightMn(a)).

When the number average molecular weight Mn(a) is less than 34000,sufficient durability cannot be secured because the wear resistancedecreases when the polyamide 66 is used in combination with aramidfiber. When the number average molecular weight Mn(a) is more than60000, it is difficult to acquire the polyamide 66 at a low cost becausesolid phase polymerization treatment or the like is necessary aftermolding. The solid phase polymerization treatment is treatment in whichthe polymerization of the resin is accelerated by exposure to ahigh-temperature condition while applying a pressure to the resincomposition in a vacuum or in an inert gas, thereby increasing themolecular weight of the resin.

The polyamide 66 having a large molecular weight can be acquired by, forexample, the following method.

(1) Commercially available polyamide 66 having a number averagemolecular weight Mn(a) of 34000 or more is acquired. Specific examplesof the commercially available product include Leona 1502S and Leona 1702(produced by Asahi Kasei Corporation) and Zytel E40, Zytel E50, ZytelE51 HSB, and Zytel E53 (produced by DuPont).

(2) Reaction is caused so as to link polyamides 66 having a numberaverage molecular weight Mn(a) of less than 34000 via a condensationagent, thereby synthesizing polyamide 66 having a large molecularweight. Any condensation agent may be used as long as the polyamides 66can be linked together. Specific examples include a compound having acarbodiimide group (—N═C═N—) (hereinafter simply referred to also ascarbodiimide). The carbodiimide may have one carbodiimide group or aplurality of carbodiimide groups. The carbodiimide may be any type ofcarbodiimide such as an aliphatic carbodiimide, an aromaticcarbodiimide, or a carbodiimide modified product. The carbodiimide maybe a macromolecular compound having a number average molecular weight of3000 to 25000.

A commercially available product may be used as the carbodiimide.Specific examples include a Stabaxol series such as Stabaxol P andStabaxol P100 (produced by Lanxess; aromatic polycarbodiimide compound),a Carbodilite series such as Carbodilite HMV-15CA (produced by NisshinboChemical Inc.; aliphatic polycarbodiimide compound), and a TCC series(produced by Teijin Limited.; cyclic carbodiimide compound).

When the condensation agent is contained, the content of thecondensation agent in the resin composition is preferably, for example,0.5 to 3.5 mass % depending on the molecular weight of the condensationagent or the like. When the content of the condensation agent is lessthan 0.5 mass %, the increase in the molecular weight of polyamide 66may fail to proceed sufficiently. When the content is more than 3.5 mass%, it is difficult to mold the jacket member stably because theviscosity of the resin composition increases.

In the resin composition, the content of the aramid fiber is 5 to 25mass %. When the content of the aramid fiber is less than 5 mass %,creep of the jacket member cannot be suppressed under high temperature(for example, 200° C.). Therefore, the sliding door cannot be paintedwith the rolling bearing for a sliding door attached to the slidingdoor. When the content of the aramid fiber is more than 25 mass %,sufficient durability cannot be secured because the wear resistancedecreases. When the content of the aramid fiber is more than 25 mass %,it is difficult to disperse the aramid fiber homogeneously in the resincomposition.

The reason why the wear resistance decreases when the content of thearamid fiber increases is presumed as follows. In the door roller inwhich the jacket member slides in a rollable manner while being in pointcontact with the mating member, when the amount of fiber in the resincomposition of the jacket member increases, the elastic modulus of theresin composition increases, and the contact pressure increases. Inaddition, when the aramid fiber itself drops off the jacket member, thearamid fiber acts as an abrasive against the jacket member. The contentof the aramid fiber is preferably 7 to 20 mass % from the viewpoint offurther reducing the possibility that the jacket member is worn.

The aramid fiber may be a para-aramid fiber or a meta-aramid fiber. Thepara-aramid fiber is preferred because the strength and stiffness of thefiber itself are high and the wear resistance is superior when thepara-aramid fiber is used in combination with polyamide 66. Although themean fiber diameter of the aramid fiber in the resin composition is notparticularly limited, the mean fiber diameter is preferably 9 to 15 μm.Although the mean fiber length of the aramid fiber is not particularlylimited, the mean fiber length is preferably 0.1 to 1 mm.

In addition to the polyamide 66 and the aramid fiber, the resincomposition may further contain other components as long as thefunctions of the polyamide 66 and the aramid fiber are not hindered. Forexample, the resin composition may contain a lubricant or a colorant.

The rolling bearing for a sliding door can be manufactured through, forexample, the following steps (1) to (3).

(1) First, a rolling bearing member including an inner ring, an outerring, rolling elements, and a cage (rolling bearing without the jacketmember of the rolling bearing for a sliding door according to thepresent invention) is manufactured by a publicly-known method.

(2) A raw material composition containing polyamide 66, aramid fiber,and the like is prepared separately from the step (1).

(3) Then, the raw material composition is subjected to injection moldingto form a jacket member on the outer peripheral surface of the outerring of the rolling bearing member.

In the step (2), the raw material composition is prepared by one of thefollowing methods.

(a) Polyamide 66 having a number average molecular weight Mn(a) of 34000or more and aramid fiber are kneaded.

(b) Polyamides 66 having a number average molecular weight Mn(a) of lessthan 34000, a condensation agent, and aramid fiber are kneaded.

It is appropriate that the raw material components be kneaded by using apublicly-known extruder (kneader) such as a twin-screw (multi-screw)extruder or a single-screw extruder.

When the raw material composition is prepared by the method (a), thepolyamide 66 has a large molecular weight. Therefore, when the rawmaterial components are kneaded so that a large amount of aramid fiberis dispersed homogeneously in the raw material composition, thepolyamide 66 may be decomposed during the kneading, and the molecularweight may decrease. Thus, when the raw material composition is preparedby the method (a), the upper limit of the content of the aramid fiber inthe raw material composition is preferably 15 mass %. This is becausethe polyamide 66 is easily decomposed during the kneading when thecontent of the aramid fiber is more than 15 mass %.

When the raw material composition is prepared by the method (b), thetrouble (decomposition of polyamide 66) that may occur when the rawmaterial composition is prepared by the method (a) is avoided. Even ifthe content of the aramid fiber contained in the raw materialcomposition is more than 15 mass %, the aramid fiber can be dispersedhomogeneously in the raw material composition. When the raw materialcomposition is prepared by the method (b), the polyamides 66 having anumber average molecular weight Mn(a) of less than 34000, thecondensation agent, and the aramid fiber may be fed simultaneously intothe extruder. It is preferable that the polyamides 66 and the aramidfiber be kneaded first and then the condensation agent be fed to furtherknead the raw material components. In this case, the molecular weight ofthe polyamide 66 is not very large during the period in which the aramidfiber is kneaded. Therefore, the aramid fiber can be dispersedhomogeneously in the raw material composition without causingdecomposition of the polyamide 66 even if the content of the aramidfiber is more than 15 mass %. After the aramid fiber is dispersed,reaction proceeds between the polyamides 66 via the condensation agent.Therefore, the aramid fiber is mixed homogeneously into polyamide 66having a large molecular weight. When the raw material composition isprepared by the method (b), a kneader having a plurality of raw materialfeed ports (feeders) is used. It is preferable that the raw materialcomposition be prepared by feeding the polyamides 66 and the aramidfiber through the same raw material feed port or different raw materialfeed ports and feeding the condensation agent through another rawmaterial feed port located on a downstream side (nozzle side) withrespect to the raw material feed port(s) where the polyamides 66 and thearamid fiber are fed.

In the step (3), the jacket member is formed by injection molding. Themethod for the injection molding is not particularly limited. It isappropriate that a publicly-known method be adopted. There is a concernthat the fluidity of the raw material composition is poor because theraw material composition contains the polyamide 66 having a relativelylarge molecular weight (particularly when the raw material compositionis prepared by the method (a) in the step (2)). In the injectionmolding, it is preferable that the following methods (A) to (C) beadopted in combination with each other as appropriate.

(A) A disk gate or a multiple-pin gate is adopted as a gate system, andthe gate diameter is increased (for example, φ0.8 mm or more, preferablyφ1 mm or more).

(B) A hot runner system is used to keep a high fluidity of the rawmaterial composition up to a point immediately behind the gate.

(C) The mold temperature is increased (for example, 100° C. or higher,preferably 120° C. or higher).

By adopting those methods in combination with each other as appropriate,the following troubles can be avoided.

The gate is sealed at an early stage, resulting in generation of vacuumvoids in the molded jacket member.

The jacket member is poor in roundness.

When the jacket member is formed in the step (3) by using the rawmaterial composition prepared by the method (b), it is preferable thatthe step (3) be carried out under the condition that the reactionproceeds between the polyamides 66 via the condensation agent even afterthe raw material composition is injected into the mold. This case issuitable to increase the fluidity of the raw material composition duringthe injection molding. As the method for achieving this condition, forexample, there may be adopted a method in which the condensation agentand the other components (polyamides 66 and aramid fiber) are kneaded ina short period of time and the injection molding is carried out promptlyafter the kneading.

Other embodiments are described below. As described in the firstembodiment, it is important that the polyamide 66 contained in thejacket member has a large molecular weight in the rolling bearing for asliding door according to the embodiment of the present invention.Instead of the number average molecular weight Mn(a) measured by themethod described in the first embodiment, the molecular weight of thepolyamide 66 may satisfy a value of a predetermined physical propertyrelated to a molecular weight measured by another method.

That is, the molecular weight of the polyamide 66 contained in thejacket member may be 53000 to 80000 as another number average molecularweight. This number average molecular weight is measured by thefollowing method. A carboxyl group of the polyamide 66 is subjected toderivatization using trifluoroacetic anhydride (TFAA) into amacromolecular compound soluble in tetrahydrofuran (THF). The obtainedmacromolecular compound is dissolved in THF, and the number averagemolecular weight is measured by gel permeation chromatography (GPC)using THF as a solvent and polystyrene (PS) as a reference material (thenumber average molecular weight measured by this method is hereinafterreferred to also as a number average molecular weight Mn(b)). Also inthis case, the jacket member contains polyamide 66 having a largemolecular weight that can attain actions and effects similar to those ofthe first embodiment of the present invention.

The polyamide 66 contained in the jacket member may have a limitingviscosity number [η] of 1.9 to 3.0 dl/g. In conformity to ISO 307, thelimiting viscosity number [η] is measured by using a micro Ubbelohdeviscometer while dissolving polyamide 66 in a solvent such as formicacid, sulfuric acid, or cresol. Also in this case, the jacket membercontains polyamide 66 having a large molecular weight that can attainactions and effects similar to those of the first embodiment of thepresent invention.

Thus, the rolling bearing for a sliding door that includes the jacketmember formed of the resin composition containing the polyamide 66 andthe aramid fiber of 5 to 25 mass % can attain actions and effectssimilar to those of the first embodiment of the present invention whenthe polyamide 66 satisfies at least one of the number average molecularweight Mn(a), the number average molecular weight Mn(b), and thelimiting viscosity number [η] within the ranges described above.

Evaluation of the rolling bearing for a sliding door using a test pieceis described below.

Test Examples 1 to 3 and Comparative Test Examples 1 to 3

A mixture of polyamide 66, aramid fiber, and a condensation agent to beadded as necessary was prepared in a composition shown in Table 1 bykneading with a twin-screw kneader TEM-26SX (manufactured by ToshibaMachine Co., Ltd.). Then, a Suzuki's friction and wear test piece inconformity to the method A of JIS K 7218 (ring-shaped test piece havingan outside diameter of 25.6 mm, a bore diameter of 20 mm, and a heightof 15 mm) was molded out of the obtained mixture by using a 100 telectric injection molding machine (manufactured by FANUC Corporation).The obtained molding was used as an evaluation test piece.

In “Test Example 3 and Comparative Test Example 3” and in “ComparativeTest Example 1 and Comparative Test Example 2”, the same types ofpolyamide 66 were adopted as raw resins, respectively.

TABLE 1 Comparative Comparative Comparative Test Test Test Test ExampleTest Example Test Example Example 1 Example 2 Example 3 1 2 3 Polyamide66 Product number Leona 1402S Leona 1402S — — — — (raw resin)Manufacturer Asahi Kasei Asahi Kasei — — — — Corporation CorporationNumber average 23000 23000 30000 or more 23000 23000 30000 or moremolecular weight Mn(a) Limiting viscosity 1.4 1.4 — 1.4 1.4 — number [η](dl/g) Aramid fiber Product number TR322U TR322U TR322U TR322U TR322UTR322U Manufacturer Teijin Limited. Teijin Limited. Teijin Limited.Teijin Limited. Teijin Limited. Teijin Limited. Addition amount 10 20 1010 20 20 (mass %) Condensation Type Aromatic CDI Aromatic CDI — — — —agent Product number Stabaxol P-100 Stabaxol P-100 — — — — ManufacturerLanxess Lanxess — — — — Addition amount 2.50 2.50 — — — — (mass %)

(1) Roller Type Friction and Wear Test (Evaluation of Wear Resistance)

As illustrated in FIG. 2, the end face of an evaluation test piece 11 isplaced on the outer peripheral surfaces of four metal rollers 12arranged horizontally on the same imaginary plane and radially at 90°with their central axes coinciding with the imaginary plane. Theevaluation test piece 11 is slid against the metal rollers by rotatingthe evaluation test piece 11 about its central axis while applying avertical load to the evaluation test piece 11. The height decreaseamount of the evaluation test piece 11 is measured after an elapse of apredetermined time. The height decrease amount of 0.05 mm or less isevaluated as “◯”, and the height decrease amount of more than 0.05 mm isevaluated as “×”. Results are shown in Table 2 nd FIG. 3.

Detailed test conditions are as follows.

-   -   Metal roller: formed of SUJ2, φ3.5 mm, four pieces    -   Lubricant: grease (produced by NOK Kluber Co., Ltd.; TOPAS NB52)    -   Sliding speed: 1 m/s    -   Test temperature: RT    -   Test time: 4 h    -   Rotation condition: intermittent rotation involving drive of        evaluation test piece about center line of bore diameter for 10        sec.⇒stop for 20 sec.

According to this friction and wear test, results correlated to thedurable life of the rolling bearing for a sliding door can be obtained.The durable life tends to increase as the height decrease amount of thetest piece decreases.

(2) Measurement of Molecular Weight of Polyamide 66

The number average molecular weight Mn(a), the number average molecularweight Mn(b), and the limiting viscosity number [η] were measured by thefollowing methods.

(2-1) Number Average Molecular Weight Mn(a)

The polyamide 66 contained in the evaluation test piece was dissolved inHFIP, and the number average molecular weight Mn(a) was measured by GPC(using PMMA as a reference material).

(2-2) Number Average Molecular Weight Mn(b)

First, a carboxyl group of the polyamide 66 contained in the evaluationtest piece was subjected to derivatization using trifluoroaceticanhydride (TFAA) into a macromolecular compound soluble intetrahydrofuran (THF). Then, the polyamide 66 subjected toderivatization by the method described above was dissolved in THF, andthe number average molecular weight Mn(b) was measured by GPC (usingpolystyrene (PS) as a reference material).

(2-3) Limiting Viscosity Number [η]

The limiting viscosity number [η] was measured by a method in conformityto ISO 307. Specifically, formic acid was selected as a solvent, and arelative viscosity η_(rel) was calculated based on a kinematic viscosityratio between the solvent and a solution of the polyamide 66 containedin the evaluation test piece and controlled at 0.005 g/l. Then, aspecific viscosity η_(sp) was calculated based on the ratio of theobtained relative viscosity η_(rel), and the specific viscosity η_(sp)was divided by a concentration c. Thus, a reduced viscosity IV and thelimiting viscosity number [η] were calculated.

TABLE 2 Comparative Comparative Comparative Test Test Test Test TestTest Example 1 Example 2 Example 3 Example 1 Example 2 Example 3Polyamide 66 Number average molecular 47000 49000 36000 25000 2700019000 (molding) weight Mn(a) Number average molecular 66000 69000 5500044000 46000 38000 weight Mn(b) Limiting viscosity number 2.5 2.6 2.0 1.51.6 1.1 [η] (dl/g) Height (mm) 0.005 0.032 0.028 0.06 0.163 0.149decrease (Evaluation) ∘ ∘ ∘ x x x amount

The evaluation results of Test Examples 1 and 3 and Comparative TestExample 1 demonstrate that the molding containing the aramid fiber of 10mass % is superior in the wear resistance as the molecular weight of thepolyamide 66 increases. The evaluation results of Test Example 2 andComparative Test Examples 2 and 3 demonstrate that even the moldingcontaining the aramid fiber of 20 mass % is superior in the wearresistance as the molecular weight of the polyamide 66 increases. InComparative Test Example 3, the polyamide 66 was decomposed during thekneading, and the molecular weight of the polyamide 66 contained in themolding (evaluation test piece) was smaller than the molecular weight ofthe polyamide 66 that was a raw resin.

The rolling bearing for a sliding door according to the presentinvention has heat resistance and creep resistance that allow thesliding door to be painted in a painting furnace, and also hassufficient durability.

What is claimed is:
 1. A rolling bearing for a sliding door, the rollingbearing being configured to be mounted on the sliding door when thesliding door is painted by passing through a high temperature paintingfurnace, the rolling bearing comprising: an inner ring; an outer ring; aplurality of rolling elements arranged in a rollable manner in anannular space between the inner ring and the outer ring; and a jacketmember formed of a resin composition and provided so as to cover anouter peripheral surface of the outer ring, wherein the jacket member isconfigured to be brought into rolling contact with a vehicle body, theresin composition contains polyamide 66 and aramid fiber, the polyamide66 has a number average molecular weight of 34000 to 60000, the numberaverage molecular weight being measured by gel permeation chromatographyusing hexafluoroisopropanol as a solvent and poly (methyl methacrylate)as a reference material, and a content of the aramid fiber is 5 to 25mass %.
 2. The rolling bearing for a sliding door according to claim 1,wherein the content of the aramid fiber is 7 to 20 mass %.